Method and apparatus for shell moulding



Dec. 27, 1955 'r. J. M LEER 2,723,122

METHOD AND APPARATUS FORQSHELL MOULDING Filed June 8, 1951 3 Sheets-Sheet 1 INVENTOR. THOMAS J MC 4552 BY l4/ MM 4 TTOEIVEYS Dec. 27, 1955 -r. .1. M LEER METHOD AND APPARATUS FOR SHELL MOULDING s Sheets-Sheet 2 Filed June 8, 1951 ATTOZ/VEYS Dec. 27, 1955 'r. J. MOLEER 2,728,122

METHOD AND APPARATUS FOR SHELL MOULDING Filed June 8, 1951 3 Sheets-She'et 3 INVENTOR. THOMAS J? 47:15:52

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United States Patent METHOD AND APPARATUS FOR SHELL MOULDING Thomas J. McLeer, Elizabeth, N. J., assignor to Cooper Alloy Corporation, a corporation of New Jersey Application June 8, 1951, Serial No. 230,556

9 Claims. (Cl. 22--3l) This invention relates to founding or metal casting, and more particularly to metal casting in shell molds.

The preparation of shell molds has been described by William W. McCulloch of the Technical Industrial Intelligence Division of the U. S. Department of Commerce in FIAT Report No. 1168 entitled, The C Process for Making Molds and Cores for Foundry Use, and since that time has been discussed in a number of periodicals and has gone into use in this country. The said process produces relatively thin or shell-like half molds which are usually held together in a box with the gate at the top and with the surrounding space filled with steel shot or similar backing material to hold the two halves together and to resist the hydrostatic pressure of the molten metal poured into the mold. This method is time-consuming and entails excessive handling of the molds and backing materials. For rapid production purposes a large investment in numerous boxes and a large quantity of shot is required.

The primary object of the present invention is to generally improve the shell molding process. A more particular object is to eliminate the need for embedding each shell mold in a box of steel shot, and to eliminate the need for any outside mechanical means for holding the half molds together. I have found that the adjacent flat surfaces or parting surfaces of the half molds may be,

adhered or cemented together with sufiicient strength to prevent separation of the half molds during the casting operation. Moreover, I have found, contrary to expectation and all past belief, that the cavity portion of the shell mold, although thin, is nevertheless strong enough to resist the hydrostatic pressure of the infiuent molten metal without reinforcing or backing the same with steel shot or other support means.

Other objects of the invention are to provide improved procedure for bonding together the molded halves; to provide a method which will be rapid, convenient, and inexpensive; and to provide accessory apparatus which may be stored with the regular metal pattern plates and used to facilitate practice of my improved process.

To accomplish the foregoing general objects, and other more specific objects which will hereinafter appear, my invention resides in the method steps and apparatus elements, and their relation one to another, as are hereinafter more particularly described in the following specification. The specification is accompanied by drawings, in which:

Figs. 1, 2 and 3 are schematic sectional views explanatory of the shell molding process for making shell half molds;

Fig. 4 is a perspective view showing a first step in the practice of my improved method;

Fig. 5 is a plan view of a half mold after the parting surface has been dusted and the stencil removed;

Fig. 6 is a perspective view showing the assembly of half molds;

Fig. 7 is a perspective view showing the non-cavity por-' tions of the half molds urged together in a press;

Fig. 8 is a detail showing one method of mounting compression springs on a plate;

Fig. 9 is a perspective view showing the pouring of molten metal through the gate and into the cavity of a shell mold;

Fig. 10 is a perspective view, drawn to smaller scale, showing a baking oven and conveyor belt which may be employed with the present process; and

Fig. 11 shows the four castings with riser and gate obtained from the particular shell mold here illustrated.

Referring to Figs. 1, 2 and 3, in accordance with the shell molding process, one first heats a metal plate 12 on which metal half patterns 14, together with any necessary risers and gates, are mounted. There are two such plates, and the shell produced from each plate fonns one-half the mold. The plate 12 is heated to say 350 or 400 F., and sprayed with a parting compound. The plate is then clamped with the pattern 14 down, on a box 16 containing an intimate mixture 18 of dry silica sand and thermosetting resin powder with a suitable accelerator. The thermosetting resin is preferably a phenol formaldehyde resin, and the accelerator is preferably hexamethylenetetramine.

The assembly shown in Fig. 1 is quickly inverted, as shown in Fig. 2, thus allowing the mixture 18 to fall down and cover the plate 12 and the patterns 14. On coming in contact with the hot plate the plastic powder softens, adjusts itself to the shape of the pattern and plate, and forms a continuous coating over the entire surface. As the material heats up the coating on the plate builds up, and after a suitable brief interval, say six seconds, this coating may reach a desired thickness of say /s". The box 16 is then again turned over or restored to its original position, as shown in Fig. 3. At this time the excess molding material 18 falls away from the soft shell mold 20, which remains on the plate 12. The excess material 18 may be used to make successive shell molds.

Sufiicient heat may be applied at this time to react and set the shell mold, but in practice it is more usual to now transfer the plate with the coating thereon to an oven Where the shell mold is heated at a temperature of about 550 F. for a suitable period of, say, two to three minutes. This may be done in any suitable oven or apparatus, and one possible apparatus is schematically shown in Fig. 10, in which a moving conveyor belt 22 runs through a tunnel-like oven 24, the top of which is banked with a large number of closely spaced infrared lamps 26. However, this is not a preferred apparatus for the purpose, because if only one metal pattern is available, and if it be preferred to heat the shell mold while it is still on the pattern plate, this additional heating step may be performed in a small stationary oven with no conveyor belt.

. In any eventthe material is cured by heat. Probably the accelerator, usually hexamethylenetetramine, liberates ammonia and formaldehyde, and the ammonia acts as a basic catalyst for the reaction between the formaldehyde and the unreacted phenol in the phenol formaldehyderesin. This results in the conversion of the material to a hard, insoluble plastic which bonds the sand grains together. On being removed from the oven the sand or baked half mold is easily stripped from the metal pattern plate by means of appropriate lifting pins or other aid, for the parting compound initially sprayed on the metal pattern plate acts as a lubricant which facilitates separation. ,The resulting half mold is a thin shell which, however, has sufiicient strength and stiffness for any necessary handling hereinafter described, and'for the casting operation.

One-half mold is preferably provided with tapered bosses, and the other with mating recesses or seats, to assure accurate alignment of the two half molds when they are placed together in face-to-face relation. Such seats are indicated at 42 in Figs. 4 and 5. As previously mentioned, the prior practice was to assemble mating half molds together; to place them in a box of sufficient size; and to fill the box around the shell mold with steel shot prior to the casting operation. In accordance with the present invention, however, the half molds are made to stick together at their flat or parting surfaces, and the casting may be poured without additionally forcing or holding the half molds together during the casting operation. For this purpose a suitable cement or adhesive is preferably applied to the parting surface of one half mold outside the cavities before adding the other half mold, and outside pressure is preferably applied to only the noncavity portions of the mold in order to avoid any possibility of damaging the convex or hollow cavity portions of the mold. l have found that a most convenient and effective way to cement the half molds together is to employ a thermosetting resin, and to use an accelerator in suitable proportion to control the reaction time, and, going even further, to employ the heat retained by the half molds as a result of the curing step to provide the heat needed to react the thermosetting adhesive.

Referring to Fig. 4 of the drawing, for a dusting step the metal pattern plates are supplemented by a suitable stencil shown at 28. This stencil may be made of thin laminated wood, or more preferably out of sheet alurnil num. For convenience it may be provided on its upper surface with suitable blocks or handles 30. The stencil has an outline corresponding to the outline of all of the cavity portions of the half mold 26, but the stencil is preferably made slightly larger than the cavity portion so that the periphery of the stencil will come outside the periphery of the cavities by a suitable amount, say one eighth of an inch. The term cavity is here used broadly to include core prints, sprues, risers and gates.

In the present case the shell mold results in a casting of the type shown in Fig. 11. The product being made is a cored body, somewhat like a valve body, and four such bodies are shown at 32 in Fig. ll. The pairs of castings are connected by a pair of risers which in turn are connected by a runner 34 and thence to a runner 36 and sprue 38, it being understood that the cast bodies 32 are subsequently broken from the risers and the remaining material, which is then re-melted for use in subsequent casting operations.

Reverting now to Fig. 4, it will be seen that the stencil 28 includes appropriate parts for covering not only the main cavities but also the sprue, riser, and gate portions of the shell mold. If the casting is cored the stencil preferably covers the core prints. in general it is so shaped as to cover all of the cavity or hollow portions of the half mold, yet preferably exposes all of the parting surface of the half mold, except for a narrow peripheral safety margin of say one eighth inch.

To help speed the process, and to help assure symmetrical or centered location of the stencil relative to the cavities therebeneath, one or more pilots may be provided. In the present case the stencil includes an extension 40 having a slightly tapered boss or projection therebeneath dimensioned to be received in one of four recesses or seats 42 which are anyway employed in the shell molding process to insure proper registration of the two halves of the mold. More than one such pilot may be employed, although in the particular case here illustrated one pilot was found adequate.

The female mold half, that is the one having recesses 42 rather than projections, is placed with its parting face uppermost, and preferably while it is still hot from the curing step, and the stencil 28 is placed in position, following which the exposed surface iscoated with adhesive. it is here dusted, through a suitable dusting sieve 44, with a mixture 46 consisting of a thermosetting resin, usually a phenol formaldehyde resin, and a suitable accelerator, usually hexamethylenetetramine, and the stencil is used because of the dusting. The stencil 28 is then removed, leaving a thin film 48 of resin on the surface of the mold surrounding the pattern cavities, as shown in Fig. 5 of the drawing. The resin may also be received in some of the seats 42, but no resin is admitted to the cavity portions of the mold.

For the present purpose the temperature of the mold is preferably 350 F. or higher, and when the powder comes in contact with the hot mold surface it becomes fluid and remains fluid for an appreciable time, the duration of which depends on the plastic composition used, the temperature, and more particularly, on the amount of the catalyst present. If the casting requires cores, the cores are next placed in the lower half mold. The upper half mold is preferably added to the dusted half mold immediately after removing the same from its pattern plate or from the supplemental heating oven, so that it too has a temperature of 350 F. or more. It is placed on the lower half mold while the dusted resin is still fluid, and the two halves are pressed tightly together by suitable mechanical means until the resin therebetween has cured and solidified.

In accordance with a feature of the present invention the half molds are preferably pressed together at the noncavity portions only, and not on the convex or cavity portions. In nearly all cases the non-cavity portions are simple fiat surfaces, and such is the case in the mold here illustrated, but it will be understood that it is not invariably true and essential that the non-cavity portions be flat, for, as is well known in foundry practice, special cases arise in which it is more convenient to curve, slope,

" offset, or otherwise vary the parting face between the two halves of a mold. It is for this reason that I refer broadly to pressing the half molds together at non-cavity portions. For this purpose I provide additional auxiliary apparatus to supplement the metal pattern plates and stencil. More specifically, I provide a bottom pressure exerting means and a top pressure exerting means which are so shaped in relation to the location of the half patterns on the pattern plates as to come outside the half patterns, or, more specifically, to come outside the cavity portions of the mold. In the preferred form here illustrated, and with reference to Figs. 6 and 7 of the drawing, the pressure is preferably applied and distributed yieldably by means of a large number of individual compression springs. For this purpose I employ a bottom plate 50 with a suitable number of compression springs 52 projecting upwardly therefrom, and a mating top plate 54 with a suitable number of compression springs 56 projecting downwardly therefrom, the said springs 52 and 56 being so located on the plates 56 and 54 as to bear against the flat portions but not the cavity portions of the half molds.

Considering the arrangement in greater detail, I find it convenient to provide a special press which in the present case comprises a table 58 with a post 6i) carrying an arm 62 (Fig. 7) which may be swung out of the way about the said post 60. The arm 62 has a cylinder 64 with a piston operating a piston rod 66 connected to an upper platen 68 to which the top pressure plate 54 is secured. The springs may be secured to the plates in any desired fashion, as by welding the ends to the plates. This has been done successfully, but requires care lest the temper of the springs be undesirably changed. Another way to secure the springs in position is to employ a small metal strap 70 (Fig. 8) over the end coil of the spring, the said strap being secured in position by suitable screw or bolt 72.

It will be understood that the bottom plate is fixedly secured in position on the table 58; that the top pressure plate 54 is fixedly secured to the top platen 68; and that the parts are superposed in registration when the arm 62 of the press is swung into working position. While the upper plate is swung out of the way, as shown in Fig. 6, the hot dusted lower half mold is placed in position on the springs 52. The cores 74 are placed in position unless that was done before transferring the half mold to the press, and the hot upper half mold 76 is placed over the lower half mold. This operation is clearly shown in Fig. 6, the operator preferably wearing asbestos gloves as indicated at 78. Variations in the procedure may be made, such as placing the lower half mold on the springs 52 before adding the stencil and dusting, or on the other hand, dusting the lower half mold, adding the cores, and adding the upper half mold, all before transferring the assembled or closed mold to the press. In general it is better not to dust in the press.

The upper plate is then swung over the lower plate, and a suitable valve is actuated to supply compressed air or hydraulic fluid to the upper half of the cylinder 64, thereby exerting a desired pressure on the flat or noncavity portions only of the mold. Inasmuch as the pressure plates with their compression springs are relatively simple and inexpensive compared to the high cost of the precision pattern plates employed in the regular shell molding process, I prefer to make upper and lower pressure plates for each metal pattern, so that the pressure plates, the stencil, and the metal pattern may all be stored, shipped or used as a unit. It would, however, be possible to employ pressure plates 50 and 54 having a large array of threaded holes for universal mounting of compression springs in any desired areas thereof, and to thus modify the number and location of the springs for each type of casting, although, as above indicated, I recommend the opposite procedure because the cost of the pressure plates, like the cost of the stencil, is minor.

It may be mentioned that it is not essential that the pressure means consist of individual compression springs. Pressure members or plates may be cut out in negative relation to the stencil shown in Fig. 4, so that the said plates will bear against the flat portions only of the mold. However, I recommend and prefer the use of individual compression springs or other such yieldable arrangement because that provides an automatic compensation for any irregularities in the thickness of the sand shell. It also takes care of special cases in which the parting surface is not a flat surface.

It may be mentioned that the lower compression springs 52 are preferably each disposed directly beneath a companion upper compression spring 56, that is, the springs are preferably alike in number and disposed in vertical alignment, so that when the press is closed the springs are directly opposed to one another and are separated by only the two solid layers of shell mold. Thus in ideal relation the springs not only do not bear against the mold cavities, but also do not bear against unsupported areas of the mold. However, this matter is not of critical importance, because the springs are yieldable and self-adjustable, and the shell mold has considerable strength.

As already indicated, the thermosetting powder which is dusted on the lower half mold is preferably so composed as to provide a liquid stage long enough to permit dusting; removal of the stencil; addition of the cores; addition of the upper half mold; and closing of the press. If the amount of catalyst or hexamethylenetetramine is too low the reaction takes place slowly, and excessive time may be required for mechanically holding the half molds together until the desired reaction is completed, that is, excessive time in the press. On the other hand, if the amount of catalyst is too high, the liquid phase may become too short. Indeed, in an extreme case the dusted powder may react and set instantaneously on contact with the hot mold, thus preventing satisfactory work. I have found that a range of from 5 to hexamethylenetetramine is satisfactory, depending in each case, of course, upon the complexity of the mold, for that affects the amount of time required to place the cores in the lower half mold and to add the upper half mold and to close the press.

In the particular case here illustrated, I have found thata total force of 1,000 lbs., exerted on pressure plates containing over thirty springs each, has proved satisfactory and has resulted in solidly joining the mold halves in a relatively short time of from one to two minutes. This permits a fairly rapid output of shell molds.

The pouring of the casting is illustrated in Fig. 9 of the drawing. For this purpose it is merely necessary to stand the completed shell molds 80, 82 and 84 on edge, with the gate portion 86 uppermost. The molds are rested directly on the foundry floor, and may be held upright in any simple and convenient fashion, as by resting a loose brick 88 on each side of the mold. It will be understood that no precaution need be taken to hold the half molds together, nor to reinforce the cavity portions, and the sole purpose of the bricks 88 is to support the molds in reasonably upright relation in order to facilitate the pouring operation. This is performed in routine fashion by using a conventional ladle 90 of molten metal 92 carried and controlled by two men holding the usual double handles at each end of rods 94. In rapid production work a long line of molds may be set up in this fashion, the ladle being carried from one mold to the next for the pouring operation.

As so far described the heat for the cementing operation is obtained by using the half molds immediately after they have been cured. This, however, is not essential,

and if desired the half molds may be permitted to cool,

and may be stored or leisurely inspected, and later reheated for the cementing operation. For some complex castings with critical requirements such careful inspection may be desirable. Any suitable oven may be employed for reheating, and one suitable arrangement is schematically illustrated in Fig. 10, for the half molds may be placed on a conveyor 22 which moves through a tunnellike oven 24 slowly enough to bring the half molds up to the desired temperature above 350 F. by the time the half molds leave the oven. They are transferred from the discharge end of the conveyor to a suitable dusting and assembly station, and then to the press, all as previously described.

It will be understood that while I have referred to the use of phenol formaldehyde resin, other thermosetting resins may be employed such, for example, as the melamine resins and the urea formaldehyde resins. Similarly, while I have mentioned the use of hexamethylenetetramine as a catalyst, any suitable catalyst may be employed to help control the reaction time. The combination of resin and catalyst is so selected and adjusted as to lower the reaction time in order to obtain maximum output of completed molds, consistent, however, with maintaining adequate operating time to take care of the necessary handling operations.

Most plastic manufacturers supply their resin with an accelerator. A commercial resin which I have found highly satisfactory for the present purpose is Resinox Industrial Resin N o. RM-1128 made by Monsanto Chemical Corporation at Springfield, Mass. This is a phenol resin with about 8 to 10% hexamethylenetetramine accelerator. I have used the said resin without alteration. I have employed other commercial thermosetting resins containing less accelerator by adding some accelerator to obtain the desired proportion. It is also possible to order a supply of thermosetting resin from a manufacturer without any accelerator at all, and to then add the desired proportion of accelerator.

It is believed that the method and apparatus of my invention, as well as the advantages thereof, will be apparent from the foregoing detailed description. It will also be apparent that while I have described the invention in preferred form, changes may be made without departing from the scope of the invention, as sought to be defined in the following claims.

I claim:

1. An accessory designed to be mounted in a power press and intended for use with shell mold parts made on metal plates having thereon metal pattern parts of less area, said accessory serving to temporarily press together and permanently adhere the shell mold parts made on said plates, said accessory comprising a bottom plate, and a mating top plate, at least one of said plates having a substantial number of compression springs projecting therefrom toward the other plate, and said springs and plates being so arranged as to hear at many points against the non-cavity portions but not the cavity portion of shell mold parts made on the aforesaid plates.

2. An accessory designed to be mounted in a power press and intended for use with shell mold parts made on metal plates having thereon metal pattern parts of less area, said accessory serving to temporarily press together and permanently adhere the shell mold parts made on said plates, said accessory comprising a bottom plate having a substantial number of compression springs projecting upwardly therefrom, a top plate having a substantial number of compression springs projecting downwardly therefrom, said top and bottom springs being substantially superposed to exert substantially directly opposed pressures, and said springs being so located on said plates as to bear at many points against the non-cavity portions but not the cavity portion of shell mold parts made on the aforesaid plates.

3. An accessory designed to be mounted on a power press and intended for use with shell mold parts made on metal pattern plates having thereon metal pattern parts of less area, said accessory serving to temporarily press together and permanently adhere the shell mold parts made on said pattern plates, said accessory comprising a bottom pressure plate, a top pressure pl te, and yieldable means associated with said pressure plates to bear yieldably at many points on the mold parts outside the cavity portion, said means being yieldable at one point relative to another and covering most of the area outside the cavity portion so that the yieldable m ans bear against the non-cavity portions but not against the cavity portion of shell mold parts made on the aforesaid plates.

4. For use in a foundry making shell molds by means of heatable shell mold pattern plates each with a metal pattern part of less area, in combination, a power press, and an auxiliary adhering device mounted in said power press and designed to be used in association with said pattern plates, said auxiliary adhering device comprising a bottom pressure exerting plate mounted on the lower part of the press, a top pressure exerting plate mounted on the upper part of the press, and yieldable means associated with said pressure plates to bear yieldably at many points on the mold parts outside the cavity portion, said means being yieldable at one point relative to another, and covering most of the area outside the cavity i portion, so that when the power press is used to press shell mold parts together when permanently adher ng them, the pressure exerting means bear against the noncavity portions but not against the cavity portion of the shell mold parts.

5. For use in a foundry making shell molds by means of heatabe mold pattern plates each with a metal pattern part of less area, in combination, a power press, and an auxiliary adhering device mounted in said power press and designed to be used n ass ciation with said pattern plates, said auxiliary adhering d vice comprisin a bottom pressure plate mounted on the lower part of the press, and a mating top pressure plate mounted on the upper part of the press, at least one of said pressure plates having a substantial number of compression springs projecting therefrom toward the other pressure plate, said springs and pressure plates being so arranged in relation to the location of the pattern parts on the pattern plates as to exert force outside the pattern parts but not on the pattern parts, and to cover most of the plate area outside the pattern parts, so that when the power press is used to press shell mold parts together when permanently adhering them, the compression springs hear at many points against the non-cavity portions but not against the cavity portion of the shell mold parts.

6. For use in a foundry making shell molds by means of heatable metal pattern plates each with a metal pattern part of less area, in combination, a power press, and an auxiliary adhering device mounted in said power press and designed to be used in association with said pattern plates, said auxiliary adhering device comprising a bottom pressure plate with a substantial number of compression springs projecting upwardly therefrom mounted on the lower part of the press, and a mating top pressure plate with a substantial number of compression springs projecting downwardly therefrom mounted in the upper part of the press, said top and bottom springs being substantially superposed to exert substantially directly opposed pressures, said springs being so located on said pressure plates in relation to the location of the pattern parts on the pattern plates as to come outside the pattern parts, so that when the power press is used to press shell mold parts together when permanently adhering them, the compression springs hear at many points against the non-cavity portions but not against the cavity portion of the shell mold parts.

7. in shell. molding, the method of making a shell mold from previously made shell mold parts having fiat portions outside of a. mold cavity portion of substantial dimension, which includes applying an adhesive to the flat portions of a shell mold part outside the cavity portion, adding the other shell mold part, rising a power press to apply simultaneously at many point a substantial outside yieldable pressure distributed over substantially all of the fiat non-cavity portions of the mold but not the cavity portion, and thus adhering the flat portions of the two mold parts to effect a sufficiently secure bond to make the mold self-supporting.

8. in shell molding, the method of making a shell mold from previously made shell mold parts having flat portions outside of a mold cavity portion of substantial dimension, which includes applying an adhesive to the fiat portions of a shell mold part outside the cavity portion, and adding the other shell mold part, while at least one of the shell mold parts is newly made and still hot with heat from its own formation, using a power press to apply simultaneously at many points a substantial outside yieldable pressure distributed over substantially all of the flat non-cavity portions of the mold but not the cavity portion, and thus adhering the flat portions of the mold parts to cifect a sufficiently secure bond to make the mold self-supporting.

9. In shell molding, the method of making a shell mold from previously made shell mold parts having fiat portions outside of a mold cavity of substantial dimension, which includes applying an adhesive to the flat portions of a mold part outside the cavity, while the said mold part is newly made and still hot with heat from its own formation, adding the other mold part while the said mold part is newly made and still hot with heat from its own formation, using a power press to apply simultaneously at many points a substantial outside yieldable pressure distributed over substantially all of the flat non-cavity portions of the mold but not the cavity portion, and thus adhering the lat portions of the two mold parts to effect a sufficiently secure bond to make the mold self-support- Qitcd in the file of this patent UNITED STATES PATENTS (Gtlier references on following page) 2,728,122 9 10 UNITED STATES PATENTS FOREIGN PATENTS 1,653,232 Smith Dec. 20, 1927 643,778 Great Britain Sept. 27, 1950 2,012,679 Craigo Aug. 27, 1935 2,354,026 Jungersen July 18, 1944 OTHER REFERENCES 2 330 751 Gowland J ly 31, 1945 5 T i al Report No. 1168, by McCulloch, pub. 2330945 3 111 7, 1945 y 1947, by Oflice of Technical Services, Dept. of 2,391,426 Kramer et a1 De 25, 1945 Commerce, Washmgton, 10 Pages. 2 41 50 Vest Feb 25 1947 The Foundry, October 1950, pages 162, 164 and 168, 2,454,712 Olsen Nov. 23, 1948 artlcle by Less- 2 47 994 Milton, In et 1 July 2 1949 10 Modern Metals, October 1950, pages 22, 23 and 24. 2,516,197 FOX July 25, 1950 2,568,364 Duesbury et a1. Sept. 18, 1951 

1. AN ACCESSORY DESIGNED TO BE MOUNTED IN A POWER PRESS AND INTENDED FOR USE WITH SHELL MOLD PARTS MADE ON METAL PLATES HAVING THEREON METAL PATTERN PARTS OF LESS AREA, SAID ACCESSORY SERVING TO TEMPORARILY PRESS TOGETHER AND PERMANENTLY ADHERE THE SHELL MOLD PARTS MADE ON SAID PLATES, SAID ACCESORY COMPRISING A BOTTOM PLATE, AND A MATING TOP PLATE, AT LEAST ONE OF SAID PLATES HAVING A SUBSTANTIAL NUMBER OF COMPRESSION SPRINGS PROJECTING THEREFROM TOWARD THE OTHER PLATE, AND SAID SPRINGS AND PLATES BEING SO ARRANGED AS TO BEAR AT MANY POINTS AGAINST 